This week the Canadian Acoustical Association is running a conference on marine and environmental sound (abstracts). Below are notes from talks that relate to the southern resident killer whales, presented in near-real-time.
9:00 Keynote: The Marine Soundscape and the Effects of Noise on Aquatic Animals
Christine Erbe
Marine soundscapes include natural sounds (e.g. from rain), marine organisms, and human sources. Christine played a wide variety of sounds from many of these sources, highlighting along the way the opportunity to listen live for southern residents in Washington State and British Columbia. Most amazing were recordings of belugas, aptly known as “sea canaries,” and humpbacks singing over mid-frequency sonar.
Odontocetes generate sound within their nasal system, not the larynx. Echolocation clicks include energy at frequencies as high as 180 kHz for some porpoises. Pile driving recorded near Australia has a power spectrum with a very broad peak centered near 200 Hz.
The effects of noise on aquatic animals can be graded from most severe to weak: damage, temporary threshold shifts, out to behavioral response.
Graded effects of noise on aquatic animals
There is little data on chronic effects of noise. We can model cumulative sound exposure, but measuring the exposure directly will be challenging. [Perhaps Marla’s recent DTAG deployments on southern residents will help calibrate models made with regional ambient noise and ship traffic data?]
10:20 How deep do you call? Depth localization in Southern Resident killer whales using passive acoustics.
Jason Wood
We recorded 189 minutes of southern resident calls and clicks as they transited Admiralty Inlet where Snohomish Public Utility District is prospecting for tidal power. We used a 4-element vertical array and localized the sound source by measuring the time of arrival differences (TOADs) between the different elements. TOADs were computed using cross-correlation for calls and hand-picking of first arrivals for clicks. The technique was validated using light bulbs as a synthetic source at known depths.
Of 510 calls and 145 independent clicks, about 80% of calls and clicks were made shallower than 30m, but some sounds (about 5%) were emitted at 60 m or deeper. So killer whales are using the full depth of the prospective tidal turbine location. Adjusting the source depths using the light bulb calibration (mean error of localization is 13 m deeper than actual bulb), our depth distribution compares well to the time-depth-recorder data from southern residents throughout their critical habitat (kindly shared with us by Robin Baird).
We also grouped our data by behavioral state of the pod during acoustic observations. One surprise was that the depth of sounds made during social behavior were significantly deeper than other behavioral states. Also, the mean depth of calls during foraging was the same as the mean depth of the clicks.
11:00 Assessing the effects of mid-frequency sonar on cetaceans in Southern California
Mariana Melcon
Looked for echolocation clicks of beaked whales (power at 30-60 kHz, depending on species) and periods of mid-frequency active sonar (MFA, 1-8 kHz) in HARP data (sampling at 200kHz). Beaked whales click 30-50% less often during MFA exposures. [Did southern residents click less during the Shoup incident?]